KINETIC STUDIES OF HUMAN BRAIN TUMORS WITH POSITRON COMPUTED TOMOGRAPHY (PCT)

Abstract

We studied 9 patients with primary and metastatic brain tumors with PCT. All subjects had kinetic F-18 fluorodeoxyglucose (FDG) studies. A modified version of the FDG model permitted estimates of the rate constants k1*, k2*, k3* and k4* as well as a fifth parameter representing cerebral blood volume (CBV). 6 subjects had CBF studies with 0–15 water, 4 subjects had CBV studies with 0–15 CO and 3 subjects had BBB kinetic studies the Ga-68 EDTA. Estimated values of CBV determined kinetically with FDG averaged 6.09 (± 1.35)cc/100gm in tumors compared to 7.47 (± 2.60)cc/100gm measured directly with 0–15 CO. The ratio of the relative CBV (determined kinetically with FDG versus directly with CO) in gray matter and tumors (compared to global values) averaged 1.02 (± 0.18) in these same 4 subjects. Simulation studies on the impact of CBV upon glucose metabolic rates (CMRG1c) determined with FDG indicated a larger overestimation of CMRG1c as CBV increased. The estimated CMRG1c determined with and without a CBV correction approached the same value in the actual patient studies as CBV decreased, in agreement with the simulation results. CBF and CMRG1c measurements together permitted calculation of net glucose extraction (GER). We found an inverse relationship between CBF and GER. Quantitative estimates of BBB permeability demonstrated no dramatic change in FDG rate constants as a function of BBB permeability changes. These studies indicate: 1) kinetic estimates of CBV in tumor and normal tissue is possible with FDG and 2) the relationships between CBF, GER and BBB permeability is quantifiable in human tumors with PCT.